1. Field of the Invention
The present invention relates to a color image forming apparatus and method usable with a color copying machine, color printer, color facsimile device, etc., having a light beam emitting mechanism for emitting plural light beams and an intermediate transfer body.
2. Description of the Related Art
Conventionally, color image forming apparatuses and methods formed a color image by using a single laser light source. In these cases, a photosensitive body moves in a subscanning direction by way of a rotational drive force created by the rotational driving section and the same body is uniformly charged by a charging mechanism. One line of laser beam emitted from the single laser light source is scanned, or moved in a predetermined direction, by a scanning mechanism, such as a rotating polygon mirror, etc., and radiated to the charged surface of the photosensitive body. Using the beam, plural color images are sequentially written on the charged surface of the photosensitive body an electrostatic latent images.
The electrostatic latent images of the plural colors thus formed are developed by plural developing media and thereby converted to respective visible toner images of plural colors. The toner images of plural colors formed on the photosensitive body are superposedly transferred respectively onto an intermediate transfer body by using a transfer mechanism. Thereby, a full-color image can be formed on the transfer mechanism.
The full-color image thus transferred onto the intermediate transfer body is further transferred onto a transfer material such as recording paper, OHP sheet, etc. and conveyed from a paper feeding apparatus by use of the (other) transfer body. The transfer material having the full-color image with the transferred image thereon is discharged from the color image forming apparatus.
Hereupon, the scanning mechanism is rotatively driven by a motor, etc. with a predetermined revolving velocity. A line synchronization signal generating mechanism detects a light beam (laser beam) from the scanning mechanism at a predetermined position and generates a line synchronization signal. The laser beam is modulated by the image signal in synchronism with the line synchronization signal, and thus the image writing operation is performed line by line.
An intermediate transfer standard signal generating mechanism detects a mark on the intermediate transfer body at a predetermined position and generates an intermediate transfer standard signal. The image forming operation of the respective colors for forming the toner images of the respective colors on the photosensitive body is performed in synchronism with the intermediate transfer standard signal.
In such an color image forming apparatus, when a high efficiency is required, it is necessary to raise the revolution rate of the scanning mechanism or the frequency of the image signal. However, the revolution rate of the scanning mechanism or the frequency of the image signal are limited and the color image forming operation could not always be preformed with the desired speed. In order to cope with such problems, there has been proposed a color image forming apparatus in the multiple-laser system having a plurality of laser light sources.
In such multiple-laser system color image forming apparatus, plural laser beams emitted from plural laser light rays are scanned by the scanning mechanism such as a polygon mirror, etc., and radiated to the charged surface of the photosensitive body. Thereby, the images are written at the same time on the photosensitive body.
The line synchronization signal generating mechanism detects the light beam from the scanning mechanism at the predetermined position and generates one line synchronization signal per light beam. The plural lines of laser beams are modulated by the image signal in synchronism with the line synchronization signal, and the writing operations of the image per plural lines are performed at the same time. Consequently, since the amount of the information to be written in on the photosensitive body is increased, the revolution rate of the scanning mechanism or the frequency of the image signal can be reduced, and thereby the stable image can be formed with high speed.
In such multiple-laser system color image forming apparatuses, since the intermediate transfer standard signal are not synchronized with the line synchronization signal, there is a probability that the higher the number of laser light sources become, an increase in phase difference between the intermediate transfer standard signal and the line synchronization signal is shifted. Thereby, the starting position of writing of the image in the sub-scanning direction shifts largely. Consequently, the color shifting (the position shifting of the toner image of the respective colors) occurs and thereby the quality of the color image deteriorates.